calculating distance

[shoobyman]

ok, i am making a spaceship/alien invader game and i am trying to create an autopilot feature. No matter what i do, the ship moves the wrong way (obviously a problem in my calculations). The ship must move away form the closest bullet, but I can't seem to do that. here is the current code. If anyone sees the problems, please tell me.

code:

if autopilot = true then         for i : 1 .. 10            %10 is the number of bullets             distx := bulletsx (i) - shipx           %The x distance away from the %current bullet it is calculating             if distx < closex then         %if the x distance is closer than the %closest x it has calculated so far, then the distx becomes the new closest %x                 closex := distx             end if         end for         if closex > 0 then   %If the closest bulletx is >0 then move away             shipx -= 5         end if         if closex < 0 then   %If the closest bulletx is <0 then move away             shipx += 5         end if     end if

help would really be appreciated

[xHoly-Divinity]

well, first of all, you should probably use pythagoran theorem for calculating distance. Since here you are doing it for 'x' coordinates only. Doesn't really matter though.

Second, you have to use an array to store distance values for every bullet. Soo... something like:

code:

var bulletdistance : array 1 .. 100 of int var highest : int for i : 1 .. 100     bulletdistance (i) := bulletsx (i) - shipx     if bulletdistance (i) > highest then         highest := bulletdistance (i)     end if end for

[xHoly-Divinity]

Sorry, the code above checks for greatest distance. If you want lowest distance, then you would check for 'less than' rather than greater than. It would make sense then if you named the variable lowestDistance as opposed to highestDistance since that is what ur lookin for :p

[shoobyman]

i have already tried your way, but the problem is your way only works for calculating the closest positive distance to a bullet. It will not work for negative bullets
THIS PROGRAM IS PISSING ME OFF!!!!!!!!!!

[richcash]

The abs () function returns the absolute value of the argument passed to it. In other words, if the parameter value is positive, it will stay the same; if it is negative, the function will return the value without the negative sign.

abs (3) is 3
abs (-4) is 4

[Clayton]

Why not just use the handy function Math.Distance(x1,y1,x2,y2 : int) ? This way you don't have to deal with negative numbers If you don't have it, make it yourself! Here's the distance formula if you dont know it:

code:

dist = sqrt((x2-x1)^2 + (y2-y1)^2)

Take if from there!

[shoobyman]

eh, i want to come up with my own formulas, it helps me learn.
I changed the code into this

code:

if autopilot = true then         for i : 1 .. 10             bulletdistance (i) := bulletsx (i) - shipx             if abs (bulletdistance (i)) < lowest then                 lowest := bulletdistance (i)             end if         end for         if lowest > 0 then             shipx += 5         else             shipx -= 5         end if         lowest := 1000     end if

Instead of running away from bullets now, it tries to get hit by them (and does a pretty good job of doing that). You would think that if i just invert the code into this:

code:

if autopilot = true then         for i : 1 .. 10             bulletdistance (i) := bulletsx (i) - shipx             if abs (bulletdistance (i)) < lowest then                 lowest := bulletdistance (i)             end if         end for         if lowest > 0 then             shipx -= 5         else             shipx += 5         end if         lowest := 1000     end if

it would work, but now it just gets stuck in the side
I hate this. I think it would help if i upload the program, so here you go.
Autopilot is automatically engaged, move around with the a,s,d,w keys.

Ignore the crappy graphics

[jrblast]

I think whats happening is that your calculating from the left side of the ship, but you should be calculating from the center of the ships x, (add picwidth(ship)div 2 to shipx in your calculations) also, what is happening by coincidence is that once it starts moving in one direction to avoid the bullets, it keeps moving because the nearest bullet is still in the same direction.

[shoobyman]

yup, i figured it out at 1:00AM last night, but it still doesn't work that good cuz it will dodge bullets only if the ship is 1 pixel wide lol, w/e